A wireless sensor network is formed by a large number of low-cost micro-sized sensor nodes deployed in a monitored area, and is a multi-hop self-organized network system that is formed in a wireless communication manner. Its objective is to collaboratively sense, collect and process information of a sensed object in a network coverage area and send the information to an observer. In the wireless sensor network, position information is of vital importance for a detecting activity of the sensor network. To determine a position where an event occurs or to obtain a node position of a message is one of the most basic functions of the sensor network, which plays a key role for the validity of a sensor network application.
Currently, a variety of positioning methods of the wireless sensor network exist, and among them a relatively common method is a positioning method based on a signal attenuation model. A basic principle of positioning performed by this method is that energy attenuates as an electromagnetic wave propagates in a space, and its attenuation amplitude is related to a propagation distance. Therefore, according to an attenuation degree of the energy of a radio wave, a distance between an emission source and a receiver may be estimated. If a position of the receiver is known, the estimated distance may be used to position the emission source. This positioning method can achieve good positioning performance in a laboratory. However, in an actual environment, conditions, such as a temperature, an obstruction, and a propagation mode, are often changing and unpredictable. Therefore, a method of simply converting measured received power into a propagation path of the electromagnetic wave through a model brings a relatively large error.
Therefore, in the prior art, a manner of a reference tag is introduced to perform assisted positioning. The reference tag refers to a node of a known and fixed position in the sensor network. For example, a LANDMARC positioning technology is a typical application of using the reference tag to perform assisted positioning. In the LANDMARC positioning technology, a certain number of radio frequency (Radio Frequency, RF) readers and a certain number of reference tags need to be deployed in a network. When positioning is performed, firstly, signal strength emitted by each reference tag and a tag to be positioned may be detected by the RF readers. Then a distance from each reference tag to the tag to be positioned is estimated according to the detected signal strength, and several (for example, three) reference tags closest to the tag to be positioned are selected as valid reference tags. Finally, a position of the tag to be positioned is determined inside a polygonal area formed by using the several valid reference tags as vertexes.
This implementation manner of performing assisted positioning by introducing the reference tag may reduce an influence of external conditions, and is more suitable for positioning in the actual environment. However, the achieving of relatively high positioning accuracy depends on deployment density of the reference tag.